Method for removing mtbe from a contaminated aqueous solution

ABSTRACT

Methods and compositions for the adsorptive removal of methyl tertiary butyl ether (MTBE) from contaminated water sources and systems. The compositions contain carbon fly ash doped with silver nanoparticles at specific mass ratios. Methods of preparing and characterizing the adsorbents are also provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional application of U.S. applicationSer. No. 14/473,702, pending, having a filing date of Aug. 29, 2014, theentire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION Technical Field

The present invention relates to methods and compositions for removal ofmethyl tertiary butyl ether (MTBE) from contaminated water sources andsystems. More particularly, the present invention relates to metalmodified carbon fly ash and methods of treating MTBE-contaminated watersources and systems with the modified carbon fly ash.

Description of the Related Art

The “background” description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description which may nototherwise qualify as prior art at the time of filing, are neitherexpressly or impliedly admitted as prior art against the presentinvention.

Methyl tertiary butyl ether (MTBE) is an established contaminant ofwater sources, following its large scale utilization as gasolineoxygenate, in replacement of tetra-ethyl lead (Rick C., Barbara R., JohnZ., (2001). National Survey of MTBE and other VOCs in CommunityDrinking-Water Sources, U.S. Geological Survey, FS-064-01—incorporatedherein by reference in its entirety. Leakage from underground storagetanks, spills during production, transportation and at gasoline fillingstations account for the major sources of environmental contamination.The high solubility of about 50,000 mg/L, low organic-carbon partitioncoefficient K_(oc) (11 mg/L) and poor natural degradation make itpersistent in the environment, as it migrates easily in the watersystem, with little tendency of being confined to the origin ofcontamination (Squillace P. J., Pope D. A., Price C. V., (1995).Occurrence of the gasoline additive MTBE in shallow ground water inurban and agricultural areas (U.S. Geological Survey Fact SheetFS-114-95, p. 4—incorporated herein by reference in its entirety)coupled with the unpleasant odor and taste introduced into thecontaminated system are the primary concerns associated with MTBE.However, the US Environmental Protection Agency considers MTBE to be apotential human carcinogen, with advisory level for MTBE ranging from 20to 40 μg/L (U.S. Environmental Protection Agency, (1997b). DrinkingWater Advisory: Consumer Acceptability Advice and Health EffectsAnalysis on Methyl Tertiary-Butyl Ether (MTBE). Washington, D.C.: U.S.Environmental Protection Agency, Office of Water,EPA-822-F-97-009—incorporated herein by reference in its entirety).

Remediation technologies such as adsorption with activated carbon orcharcoal filters, air stripping, and ultraviolet/hydrogen peroxide(Fenton) treatment have recorded varying levels of success with MTBE.However, each technique is characterized by its inherent limitations,which creates the continuous need for improvements in the removal ofMTBE from contaminated water sources. Adsorption based treatments ofMTBE contaminated systems face a major challenge from the highsolubility and low organic-carbon properties of MTBE. However, granularactivated carbon has recorded significant success in removal of MTBEfrom aqueous solution, hence regarded as the established adsorbent ofMTBE (Sutherland J., Adams C., Kekobad J., (2004). Treatment of MTBE byair stripping, carbon adsorption, and advanced oxidation: technical andeconomic comparison for five groundwaters, Water Research, 38(1), pp.193-205—incorporated herein by reference in its entirety). Impregnationof adsorbent materials with selected metal oxides has been reported toimprove their adsorption efficiencies, as several studies have shown forimpregnated activated carbon and other low surface area materials likefly ash (Wan Ngah, W. S., and Hanafiah, M. A. K. M. (2008)). Removal ofheavy metal ions from wastewater by chemically modified plant wastes asadsorbents: a review. (Bioresource technology, 99(10),3935-3948—incorporated herein by reference in its entirety). Scientificstudies into the use of readily available low cost materials for theremoval of environmental contaminants such as heavy metals and otherorganic pollutants have gained significant attention.

Fly ash (FA) constitutes the major particulate waste by-product duringthe generation of electricity by burning of coal or heavy liquid fuel.Fly ash is generated as a non-combustible, fine residue, carried in theflue gas and usually collected with the aid of electrostaticprecipitators, and having a uniform size distribution of particlesranging 1 to 10 μm (Khairul N. I., Kamarudin H. and Mohd S. I. (2007).Physical, chemical & mineralogical properties of fly ash. Journal ofNuclear and Related Technology 4, 47-51—incorporated herein by referencein its entirety). Presently, the major applications of fly ash are insoil stabilization and as additives in the manufacturing of cements,with a large proportion of the fly ash material being disposed by landfilling. The potential for utilizing fly ash as an inexpensive adsorbentwas driven by its high alumina and silica content, where it could beadopted as liner for landfills to minimize leachate of organicpollutants (Mott H. V., Weber W. J. (1992). Journal of EnvironmentalScience and Technology, 26, pp 1234—incorporated herein by reference inits entirety).

Application of fly ash as adsorbent of contaminant in aqueous solutionis considered to be an alternative form of waste management, in place ofthe disposal in landfills. Raw fly ash and other modifications to ithave been assessed for their removal efficiencies of severalenvironmental contaminants in previous studies (Yadla, S. V., Sridevi,V., & Lakshmi, M. C. (2012). Adsorption performance of fly ash for theremoval of lead. International Journal of Engineering Research &Technology, 1(7); Visa, M., & Duta, A. (2013). Methyl-orange and cadmiumsimultaneous removal using fly ash and photo-Fenton systems. Journal ofhazardous materials, 244, 773-779; Ragheb, S. M. (2013). Phosphateremoval from aqueous solution using slag and fly ash. HBRC Journal,9(3), 270-275—each incorporated herein by reference in its entirety).However, their capacity for removal of MTBE from aqueous solutionremains unsubstantiated.

In view of the foregoing, it will be advantageous to design methods andcompositions that can efficiently treat MTBE contaminated water systemsat a low economic cost. Disclosed embodiments of the present inventionovercome the shortcomings of the prior art as described herein.

BRIEF SUMMARY OF THE INVENTION

The foregoing paragraphs have been provided by way of generalintroduction, and are not intended to limit the scope of the followingclaims. The described embodiments, together with further advantages,will be best understood by reference to the following detaileddescription taken in conjunction with the accompanying drawings.

In a first aspect, the present invention relates to adsorption methodsfor removing methyl tertiary butyl ether (MTBE) from an aqueous solutioncomprising contacting a composition comprising carbon fly ash and metalnanoparticles with the aqueous solution. The metals can be silver, zinc,copper, nickel, chromium, iron. In a preferred embodiment, the metal issilver. Described methods can efficiently remove at least 10% MTBE fromthe treated aqueous solution.

The carbon fly ash and the metal nanoparticles are present in thecomposition at 50-90% and 10-50% by mass, respectively.

The disclosed MTBE adsorption methods are carried out under agitationconditions to provide improved adsorption.

An effective dosage of the composition is in the range of 10 mg to 100mg per 10⁻³ ppb of MTBE.

In a second aspect, the present invention relates to compositions foradsorbing and removing methyl tertiary butyl ether (MTBE) from anaqueous solution comprising carbon fly ash particles and metalnanoparticles. In one embodiment, the carbon fly ash and the metalnanoparticles are present in the composition at 50-90% and 10-50% bymass, respectively. In another embodiment, the preferred metal issilver.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1A illustrates the thermo-gravimetric analysis results for 7 mg rawfly ash in alumina pan, at temperature 10° C./min to 800° C. and air asflow gas with a flow rate of 100 mL/min.

FIG. 1B illustrates the thermo-gravimetric analysis results for 7 mgacid-treated fly ash in alumina pan, at temperature 10° C./min to 800°C. and air as flow gas with a flow rate of 100 mL/min.

FIG. 1C illustrates the thermo-gravimetric analysis results for 7 mgsilver nanoparticles doped fly ash in alumina pan, at temperature 10°C./min to 800° C. and air as flow gas with a flow rate of 100 mL/min.

FIG. 2A is an SEM micrograph of carbon fly ash (500× magnification).

FIG. 2B is an SEM micrograph of silver nanoparticles doped carbon flyash (500× magnification).

FIG. 3A is an EDX spectrum of carbon fly ash.

FIG. 3B is an EDX spectrum of acid treated carbon fly ash.

FIG. 3C is an EDX spectrum of silver nanoparticles doped carbon fly ash.

FIG. 4 illustrates the effect of agitation speed on MTBE removalefficiency at room temperature, pH 6, 2 hrs contact time, and 1000 ppbinitial MTBE concentration.

FIG. 5 illustrates the effect of adsorbent dosages (mg) on MTBEadsorption behavior of different fly ash materials at room temperature,200 rpm, pH 6, 2 hrs contact time, and 1000 ppb initial MTBEconcentration.

FIG. 6 illustrates the effect of contact time on MTBE adsorptionbehavior of fly ash based adsorbents at room temperature, 200 rpm, pH 6and 1000 ppb initial MTBE concentration.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Referring now to the drawings, wherein like reference numerals designateidentical or corresponding parts throughout the several views.

The present invention is directed to methods and compositions forremoving MTBE from contaminated water sources and systems. Examples ofsuch water sources and systems include, but are not limited to, surfacewater that collects on the ground or in a stream, aquifer, river, lake,reservoir or ocean, ground water that is obtained by drilling wells,run-off, industrial water, public water storage towers, publicrecreational pools and bottled water.

In one embodiment, the present invention relates to carbon fly ash basedadsorbents for the removal of MTBE. The fly ash may be produced from thecombustion of coal, liquid fuels or co-combustion of petroleum coke andcoal. The fly ash generated from these combustions may be recovered forrecycling by power plants.

Not all fly ash produced from combustions can be used as adsorbents. Flyash from combustions described above (i.e. carbon fly ash) with a carboncontent of at least 65% and having good adsorption properties issuitable for the purposes of the present invention. With carbon as theprimary component, other components of carbon fly ash may includeoxygen, sulfur, zinc, copper, minerals, metals, main group elements,SiO₂, FeO⁴⁻, Fe₂O₃, Al₂O₃, CaO, MgO, CO₂, Na₂O, and/or water. Sources ofcarbon fly ash include coal power stations, wherein the carbon fly ashis captured from the flue gaseous effluent. Rather than being discardedas wastes into landfills and ash ponds, carbon fly ash wastes may betransported to beneficiation plants for recycling and further processingfor secondary uses.

The raw carbon fly ash used in various embodiments of the presentinvention may have a BET surface area of 1-20 m²/g, preferably 5-10 m²/gor about 7 m²/g. The particles are generally spherical in shape andrange in size from 0.5 μm to 300 μm, preferably no greater than 100 μmor about 50 μm. In a preferred embodiment, carbon fly ash nanoparticlesare used to make the MTBE adsorbents in the present invention, havesizes with the ranges of 2500-10000 nm, 5000-8000 nm, preferably100-2500 nm, or about 1000 nm.

In one embodiment, the raw carbon fly ash may be treated with an acidsuch as HNO₃, HF, HCl and H₂SO₄. The acid treatment may enhance theadsorption properties of the carbon fly ash. The raw carbon fly ash mayalternately be treated with a base such as NaOH to affect the pore sizeand/or surface characteristics.

In one embodiment, the raw carbon fly ash may be modified with at leastone metal oxide, for example, oxides of silver, zinc, copper, nickel,chromium, iron or any metal of low cost and low toxicity. Themodification is for the purpose of increasing the surface area of carbonfly ash in order to increase its MTBE adsorption efficiency. Preferably,carbon fly ash may be impregnated with nanoparticles of a metal oxidewherein the nanoparticles bind to the surface and pore space of the flyash material.

In one embodiment, the metal oxide is silver oxide (AgO).

In one embodiment, the metal nanoparticles are 1-10 nm in diameter,preferably no greater than 5 nm or about 2 nm.

Also provided are methods of loading the metals onto the raw carbon flyash. Such methods include direct doping with a stable salt containingthe desired metal, wet impregnation, hydrolysis impregnation andchemical vapor deposition (CVD).

In one embodiment, the modification of carbon fly ash with a metal oxidemay increase the surface area of the fly ash particles by at least 100%(or at least 15 m²/g), preferably 125-150% (or 15-17.5 m²/g), 150-175%(or 17.5-19 m²/g) or 175-200% (or 19-20 m₂/g).

Metal oxide nanoparticles and carbon fly ash are combined at specificmass ratios. In one embodiment, the ratio of the fly ash to metal is9:1. In another embodiment, the ratio may be 8:2, 7:3, 6:4 or 5:5.

In one embodiment, metal oxide nanoparticles and carbon fly ash arepresent in the composition at 50-90% and 10-50% by mass, respectively,based on the total weight of the composition.

Methods of removing MTBE according to the present invention includecontacting the metal oxide modified carbon fly ash withMTBE-contaminated water sources and systems. These methods may becarried out in tanks, containers or small-scale applications. Beforetreatment, an exemplary water sample may have MTBE concentrations of10⁻⁶ to 10⁻¹ ppb, preferably 10⁻⁵ to 10⁻² ppb or 10⁻³ ppb. Effectiveadsorbent dosages corresponding to the MTBE concentrations may be 0.1 mgto 1 g, preferably 10 mg to 100 mg or 50 mg. MTBE is removed byadsorption, which means the process is physical and no chemical changes,such as oxidation, are made upon MTBE. Contacting is carried out at aconvenient temperature lower than the boiling point of MTBE at standardpressure.

The treatment process may run for as long as 30 mins or up to 5 hrs,preferably 1 to 3 hrs or 2 hrs. The duration needs to be long enough toensure sufficient contact time between adsorbent materials and MTBEcompounds. However, if the process is left to run for too long,desorption may start to occur, resulting in the bound MTBE moleculesbeing released from the metal oxide modified carbon fly ash compositeparticles.

In certain embodiments, the treatment process may be enhanced withmechanical shaking. Agitation speeds of 20-350 rpm, preferably 50-250rpm or 200 rpm may be introduced to the reaction in order to increasecontact between adsorbent and adsorbate (MTBE) materials. At agitationspeeds of higher than 350 rpm, adsorbent materials may volatilize.

At least 10% of the total mass of MTBE may be removed by the treatmentmethods described herein, preferably 20-30% or 25%. It is especiallypreferred that at least 50%, more preferably at least 60%, 80% or 90% ofthe MTBE of an MTBE-contaminated sample is removed by adsorption of theMTBE using the treatment methods described herein.

The examples below are intended to further illustrate protocols forpreparing and assessing the adsorbent materials for MTBE removalefficiency described herein, and are not intended to limit the scope ofthe claims.

Example 1 Chemicals

The MTBE used in various embodiments of the present invention waspurchased from Sigma-Aldrich, Saudi Arabia, with 99.999% purity (HPLCgrade). Deionized water from Mili-Q direct purification system was usedfor preparation of 100 ppm MTBE stock solutions, from which water wasspiked prior to treatment. Silver nitrate (AgNO₃) from EurostarScientific Company was used as sources of the silver nanoparticles,ethanol from Sigma-Aldrich with 99.8% purity and nitric acid from LOBAChemic PVT Ltd were also utilized in the embodiments described herein.

Example 2 Preparation of Adsorbent Materials

The fly ash used in this study was obtained from a local powergenerating plant that has been collected by electrostatic precipitatorduring the burning of heavy liquid fuel. The raw fly ash was treatedwith nitric acid in the volume ratio of 1:3 (ash: nitric acid). Themixture was stirred for 24 hrs at 120° C., with an attached condenser.Segregation of phases was ensured by allowing the mixture to stand for 2hrs, after which the acid was decanted and the slurry phase was washedwith deionized water. The washing process was repeated until the pH ofthe waste water reached the level of that of the original deionizedwater used. Subsequently, the slurry phase was oven dried at 100° C. for24 hrs and stored until used for the batch experiments.

A 10% (by mass) silver nanoparticle doping was carried out using silvernitrate (AgNO₃) as source. Subsequently, 90% carbon fly ash of totalmass was added and soaked in ethanol. Sonication of the mixture wasperformed for 30 mins, before calcination at 350° C. for 3 hrs (Keith,C. H. (1967). U.S. Pat. No. 3,355,317—incorporated herein by referencein its entirety) and the resultant material stored until used for batchadsorption experiment.

Example 3 Adsorption Experiments

Each of the batch experiments was carried out in a 125 mL conical flaskwith a Parafilm sealing membrane. For each of the experimentsappropriate amount of the adsorbent materials and 100 mL of 1000 ppbinitial concentration MTBE spiked solution were added to the conicalflask. Blank experiments were conducted to assess the loss of adsorbateto the flask and environment during the sorption process. Differentdosages of the adsorbent materials, ranging from 10 mg to 100 mg wereused for the sorption tests. A mechanical shaker was used for generatingcontact in the flask at varied agitation speeds (50 to 200 rpm) andcontact time from 1 to 5 hrs. Duplicate 1.0 mL water samples werecollected at one hour interval for 5 hrs in a glass vial and analyzedfor MTBE concentration using GC/MS system. A gas chromatography coupledwith ISQ single quadrupole mass spectrometer system, fitted with aTriplus headspace injector unit and an auto-sampler was used. A fusedsilica capillary column was used in the unit (60 m length, 0.32 mminternal diameter and 1.80 μm thickness). While the carrier gas washelium at 1.7 mL/min constant flow rate, selected ion monitoring (SIM)mode was used to obtain the ion current at the mass to charge ratio ofinterest, having set the mass range at 72.50-73.50 for MTBE.

Example 4 Physical and Chemical Characterizations of the PreparedAdsorbents

The results obtained from a variety of relevant instrumental studies ofthe adsorbent materials, to offer insights into the surface morphology,surface area, elemental composition and mechanism of MTBE removal fromthe solution, are laid out in the following examples.

Example 5 Thermo-Gravimetric Analysis of the Prepared Adsorbents

The results from the thermo-gravimetric analysis (TGA) of the adsorbentmaterials, as shown in FIG. 1A, show that fly ash was completely burntat approximately 600° C. with less than 5% impurity remaining beyondthis temperature. However, following acid treatment of the fly ashmaterials, no residual impurity was observed as the residual material'sweight dropped to 0%. (see FIG. 1B) For the metal oxide impregnations,90% (by weight) of fly ash was used in the preparation of theadsorbents, and approximately 80% (by weight) was recovered aftercalcination as shown in FIG. 1C.

Example 6 Brunauer, Emmett and Teller (BET) Surface Area Analysis of thePrepared Adsorbents

BET specific surface areas of the prepared FA based adsorbents weredetermined by N₂ adsorption analysis using a Micromeritics model ASAP2010 analyzer. Prior to the measurements, the samples were degassed at250° C. under nitrogen flow for 6 hrs in order to remove moisturecompletely. Physical adsorption of N₂ was carried out in a liquidnitrogen bath maintaining 77 K temperature.

Silver oxide which is the doped silver nanoparticle used in the presentinvention was for the purpose of increasing the surface area of thecarbon fly ash, thereby increasing its MTBE adsorption efficiency. Theresults BET analysis of the adsorbent materials as summarized in Table 1showed approximately 100% increase in the surface area of the carbon flyash following silver oxide impregnation.

TABLE 1 Brunauer Emmett Teller (BET) surface area analysis of FA basedadsorbents. BET surface area Adsorbent (m²/g) Raw fly ash 7.1539 Acidtreated fly ash 6.0245 Silver oxide impregnated fly ash 16.7890

Example 7 Scanning Electron Microscopy (SEM)-Energy Dispersive X-Ray(EDX) Analysis of the Prepared Adsorbents

The SEM micrograph (500× magnification) of the raw fly ash material inFIG. 2A, shows the orbicular structure of the fly ash powder, havingapproximately 100 μm average grain diameter, with pores of differentsizes on its surface. Also, the distribution of the silver nanoparticleson the surface of the fly ash, following impregnation and binding of themetal oxides to the pore spaces on the fly ash material (see FIG. 2B)

The micro-chemical analysis of raw fly ash material showed the adsorbentto be mainly composed of carbon, with considerable amount of oxygen asshown in the EDX spectra in Table 2, FIGS. 3A, 3B, and 3C. The spectrain FIGS. 3A, 3B, and 3C also showed that acid treatment of the fly ashresulted in removal of vanadium and decrease in sulfur composition ofthe fly ash material.

TABLE 2 Energy Dispersive X-ray spectroscopy of FA based adsorbents.Acid Treated Raw FA FA Ag₂O-FA Element Weight % Carbon (C) 78.1  80.276.3 Oxygen (O) 11.6  13.4  7.8 Sulfur (S) 7.1  6.4  5.3 Zinc (Zn) 1.4 —— Copper (Cu) 1.3 — — Vanadium (V) 0.5 — — Silver (Ag) — — 10.6

Example 8 Effects of Treatment Parameters on MTBE Removal

To understand the conditions under which MTBE is removed from theaqueous solution, treatment parameters such as agitation speed,adsorbent dosages and contact time were varied and their impacts on theremoval efficiency were noted in the examples described below.

Example 9 Effect of Agitation Speed on MTBE Removal Efficiency

Adsorption, being the mechanism of treatment used in this study,required contact between the surface of the adsorbent material and thetarget adsorbate (MTBE). To understand the role of agitation speed, thebatch experiment was conducted at speeds from 50 to 200 rpm. FIG. 4shows an increase in the removal efficiency with increase in agitationspeed till 200 rpm. The poor removal of MTBE at lower agitation speedcan be attributed to lack of contact between the active adsorption siteson the fly ash and the MTBE solution, as the adsorbents were settled atthe base of the conical flask. However, the speed was not increasedbeyond 200 rpm in order to minimize loss by volatilization during theagitation process. Hence, subsequent batch experiments were conducted at200 rpm.

Example 10 Effect of Adsorbent Dosage on MTBE Removal Efficiency

Several adsorption studies have shown the adsorbent dosage to influencethe adsorbate removal efficiencies, because it determines the adsorptioncapacity of adsorbents based on the number of adsorption sites available(Etim, U. J., Umoren S. A., Eduok U. M. (2012). Coconut coir dust as alow cost adsorbent for the removal of cationic dye from aqueoussolution, Journal of Saudi Chemical Society—incorporated herein byreference in its entirety). FIG. 5 shows that with the exception ofsilver nanoparticles doped carbon fly ash, there was no significantvariation in the percentage removal of MTBE for all other fly ash basedadsorbent materials tested, with change in dosage. Silver oxideimpregnated fly ash showed an increase in adsorption with increase indosage of adsorbent material until a peak dosage was reached, beyondwhich a slight decrease in adsorption was observed with increase inadsorbent material. A peak reduction of 24% was noted at 50 mg ofadsorbent and further increase in adsorbent resulted in decline inadsorption. The availability of more adsorption sites due to increase inadsorption surface area can be presumed responsible for the increase inMTBE adsorption with increase in adsorbent dosage (SenthilKumar, P.,Ramalingam, S., Senthamarai, C., Niranjanaa, M., Vijayalakshmi, P.,Sivanesan, S., (2010). Adsorption of dye from aqueous solution by cashewnut shell: studies on equilibrium isotherm, kinetics and thermodynamicsof interactions. Desalination 261, pp. 52-60—incorporated herein byreference in its entirety). The decline in adsorption with increase indosage beyond 50 mg can be attributed to overlapping or aggregation ofadsorption sites resulting in reduction in the surface area availablefor MTBE adsorption, with El-Sayed et al. reporting similar behavior inan adsorption study of methylene blue (El-Sayed, G. O., (2011). Removalof methylene blue and crystal violet from aqueous solutions by palmkernel fiber. Desalination 272, pp. 225-232—incorporated herein byreference in its entirety).

Example 11 Effect of Contact Time on MTBE Removal Efficiency

In most adsorption studies, the adsorption time requirements vary basedon the nature of interaction occurring between the adsorbent andadsorbate. FIG. 6 shows that the adsorption of MTBE by silvernanoparticles doped carbon fly ash (irrespective of dosage) increasedwith time till 2 hrs of contact with the adsorbent, after which therewas a slight and gradual decline in the adsorption. This observation canbe explained by the adsorption equilibrium phenomenon, in which the rateof adsorption was greater than the rate of desorption until equilibriumwas reached at the contact time of 2 hrs, at which the adsorption siteson the adsorbent were saturated. Beyond this point, the rate ofdesorption was greater than the rate of adsorption, accounting for theslight and gradual decline in the MTBE adsorption beyond the optimumtime of 2 hrs.

Thus, the foregoing discussion discloses and describes merely exemplaryembodiments of the present invention. As will be understood by thoseskilled in the art, the present invention may be embodied in otherspecific forms without departing from the spirit or essentialcharacteristics thereof. Accordingly, the disclosure of the presentinvention is intended to be illustrative, but not limiting of the scopeof the invention, as well as other claims. The disclosure, including anyreadily discernible variants of the teachings herein, defines, in part,the scope of the foregoing claim terminology such that no inventivesubject matter is dedicated to the public.

1-9. (canceled)
 10. A method for removing MTBE from an MTBE-contaminatedaqueous solution, comprising: forming acid-treated fly ash particles bystirring a raw fly ash with nitric acid to form a slurry; and washingthe slurry to produce the acid-treated fly ash particles which consistof carbon, oxygen, and sulfur; doping the acid-treated fly ash particleswith AgNO₃ and calcining to form a composition comprising theacid-treated fly ash particles and silver oxide nanoparticles havingdiameters in a range of 1-10 nm; wherein the silver oxide nanoparticlesare present on the surface and in pore spaces of the acid-treated flyash particles; wherein the composition is in the form of particleshaving sizes in a range of 100 nm to 2.5 μm and a BET surface area of atleast 16.789 m²/g, wherein the acid-treated fly ash particles and thesilver oxide nanoparticles are present in the composition at masspercentages of 50-90% and 10-50%, respectively, based on the totalweight of the composition; contacting the MTBE-contaminated aqueoussolution with the composition to adsorb the MTBE and form a purifiedaqueous phase; then separating the purified aqueous phase from thecomposition. 11-13. (canceled)
 14. The method of claim 10, wherein theacid treated fly ash particles consist of 80.2 wt % carbon, 13.4 wt %oxygen, and 6.4 wt % sulfur, each relative to a total weight of theacid-treated fly ash.
 15. The method of claim 10, wherein thecomposition consists of acid-treated fly ash particles and silver oxidenanoparticles.
 16. The method of claim 10, wherein the compositionconsists of 76.3 wt % carbon, 7.8 wt % oxygen, 5.3 wt % sulfur, and 10.6wt % silver oxide nanoparticles, each relative to a total weight of thecomposition.